Method for decomposing polysulfone

Abstract

To provide an effective decomposition method for recycling and up-cycling polysulfone belonging to super engineering plastics and described to be applied to a wide range of uses.SOLUTION: This method for decomposing the polysulfone comprises heating the polysulfone in the presence of an N-heterocyclic carbeneborane in a solvent by using a radical initiator and a base.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for decomposing polysulfone. [Background technology]

[0002] Polysulfone is a polymeric compound with repeating units containing sulfonyl groups, and because it possesses mechanical strength, heat resistance, hydrolysis resistance, flame retardancy, chemical resistance, electrical properties, transparency, weather resistance, and ease of moldability, it is classified as a super engineering plastic and is expected to be used in a wide range of applications. However, due to the high cost of raw materials and processing costs, its use is currently limited to specialized applications. For this reason, there has been an increasing demand in recent years for the recycling and upcycling of polysulfone waste, and the reuse of discarded polysulfone is being considered.

[0003] Polysulfone has excellent chemical resistance, heat resistance, etc., and therefore has been a polymer compound that is extremely difficult to chemically decompose. Recently, a decomposition reaction of super engineering plastics containing polysulfone under mild conditions has been reported (Non-Patent Document 1). However, the reported decomposition method involves cleaving the carbon-oxygen bond of polysulfone to decompose it into raw material monomers, and the obtained raw material monomers can be converted back into polysulfone by repolymerizing them. In other words, the reported decomposition method makes it possible to recycle polysulfone, but upcycling is difficult.

[0004] Due to the unique electronic properties of the boron atom, organoboron compounds have attracted attention in various fields, such as medicine, agrochemistry, and materials chemistry. Based on this understanding, the present inventors have developed an efficient method for synthesizing organoboron compounds by reacting N-heterocyclic carbene borane with an aryl sulfone, a radical initiator, and a base. They have discovered that NHC-aryl-substituted borane compounds can be obtained by reacting N-heterocyclic carbene borane (NHC) with an aryl sulfone in the presence of a radical initiator. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Minami, Y.; Inagaki, Y.; Tsuyuki, T.; Sato, K.; Nakajima, Y. ,Hydroxylation-Depolymerization of Oxyphenylene-Based Super Engineering Plastics To Regenerate Arenols, JACS Au 2023, 3, 2323-2332. https: / / doi.org / 10.1021 / jacsau.3c00357. Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide an effective decomposition method for recycling and upcycling polysulfone, which belongs to the super engineering plastic category and is expected to be used in a wide range of applications. [Means for solving the problem]

[0007] The present inventors have been conducting research into N-heterocyclic carbene boranes (NHCs) and aryl sulfones, and have found that the decomposition reaction of polysulfone proceeds when polysulfone is heated using di-tert-butoxy peroxide as a radical initiator, potassium carbonate as a base, and o-xylene as a solvent in the presence of N-heterocyclic carbene borane. This finding led to the completion of the present invention.

[0008] That is, the present invention relates to what is specified by the following items. [1] A method for decomposing polysulfone by heating polysulfone in the presence of N-heterocyclic carbene borane in a solvent using a radical initiator and a base. [2] The decomposition method according to [1], wherein the radical initiator is di-tert-butoxy peroxide. [3] The decomposition method according to [1], wherein the base is potassium carbonate. [4] The decomposition method according to [1], wherein the solvent is o-xylene. [5] The decomposition method according to [1], wherein the N-heterocyclic carbene borane is a compound represented by the following formula: [ka] [Effects of the Invention]

[0009] According to the decomposition method of the present invention, polysulfone is not decomposed into monomers, but rather the sulfur-carbon bonds of polysulfone are cleaved to generate new decomposition products having carbon-boron bonds. This enables various molecular exchanges utilizing the carbon-boron bonds, making it possible not only to recycle but also to upcycle polysulfone. [Brief explanation of the drawings]

[0010] [Figure 1] 11B-NMR spectrum showing the formation of ArBH2NHC. [Figure 2] SEC spectrum showing the disappearance of polysulfone and the appearance of new peaks in the low molecular weight region. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention relates to a method for decomposing persistent polysulfone, and more particularly to a method for decomposing polysulfone by heating the polysulfone in the presence of an N-heterocyclic carbene borane in a solvent using a radical initiator and a base.

[0012] The polysulfone of the present invention is not particularly limited as long as it is a polymer compound having a repeating unit containing a sulfonyl group, and is not limited to polysulfone but also includes polyethersulfone. Furthermore, polyphenylene sulfide may also be subject to the decomposition method of the present invention by oxidizing the sulfide groups to sulfonyl groups. The polysulfone of the present invention is typically represented by the following chemical formula: [ka]

[0013] The decomposition method of the present invention uses a radical initiator, and examples of the radical initiator include peroxide initiators such as di-tert-butoxy peroxide, azo initiators such as azoisobutyronitrile (AIBN), 2,2'-azobis(isobutyrate)dimethyl, and di-t-butyl hyponitrite, and initiators that react with light irradiation such as diphenyl disulfide. Although there are no particular limitations, peroxide initiators are preferred, such as di-tert-butoxy peroxide. The radical initiator can be used in the range of 0.1 to 1.0 equivalents relative to the polysulfone, and preferably 0.2 equivalents.

[0014] The decomposition method of the present invention uses a base, and the base is not particularly limited, but examples include NaOt-Bu, NaOH, K3PO4, K0t-Bu, KOH, K2CO3, Cs2CO3, Na2CO3, and CsOH·H2O, with potassium carbonate (K2CO3) being preferred. The base can be used in an amount ranging from 1.2 to 2.4 equivalents relative to the polysulfone, with 2.4 equivalents being preferred.

[0015] The decomposition method of the present invention is carried out in a solvent, and the solvent is not particularly limited, and examples thereof include o-xylene, toluene, t-butanol, benzotrifluoride, and m-xylene, with o-xylene being preferred.

[0016] In the decomposition method of the present invention, a compound represented by the following chemical formula was used as the N-heterocyclic carbene borane (NHC-BH3): In the decomposition method of the present invention, the N-heterocyclic carbene borane can be used in an amount of 1 to 15 equivalents, preferably 2 to 12 equivalents, 3 to 10 equivalents, 4 to 10 equivalents, 5 to 10 equivalents, or 5 to 8 equivalents, relative to the polysulfone. [ka]

[0017] The decomposition method of the present invention involves heating, and can be carried out at a heating temperature in the range of about 120 to 150° C. It is preferable to stir the mixture during heating, and any stirring means can be used for stirring.

[0018] It was confirmed that the decomposition method of this invention cleaves the sulfur-carbon bond of polysulfone, producing a compound in which the aryl group obtained by cleavage is bonded to BH2NHC. Compounds in which an aryl group is bonded to BH2NHC can be converted into various compounds, such as by introducing an aryl group via the Suzumi-Miyaura reaction or by converting them to phenols via oxidation, making upcycling based on the decomposition of polysulfone possible.

[0019] The present invention will be specifically described below with reference to examples of the present invention, but the technical scope of the present invention is not limited to these examples. [Example]

[0020] Polysulfone (227.6 mg, 0.51 mmol, 1 equivalent) was added to o-xylene (1.5 mL) in a pressure tube and heated until dissolved. N-heterocyclic carbene borane (273.3 mg, 2.49 mmol, 5 equivalents), potassium carbonate (K2CO3 (166.1 mg, 0 mL, 1.2 mmol, 2.4 equivalents)), and di-tert-butoxyperoxide (15.2 mg, 0 mL, 0.1 mmol, 0.2 equivalents) were added, and the mixture was purged with nitrogen and stirred at 140°C for 24 hours. After stirring, methanol was added, and the supernatant and precipitate were separated. The polysulfone sample used was polysulfone manufactured by Acros Organics with a weight-average molecular weight of 60,000 (catalog value). The reaction in Example 1 is summarized by the following chemical reaction formula. [ka] The resulting supernatant and precipitate were subjected to solvent removal using an evaporator and a vacuum pump, respectively, to obtain a supernatant (578.5 mg) and a precipitate (149.2 mg). H-NMR, B-NMR, and SEC were performed on each. B-NMR revealed a peak at -26 ppm (t, J = 85 Hz) attributable to the compound (ArBHNHC) formed by the cleavage of the sulfur-carbon bond in polysulfone, resulting in the formation of an aryl group (Ar) bonded to an N-heterocyclic carbene borane (NHC-BH). The B-NMR spectrum is shown in Figure 1. Furthermore, size exclusion chromatography (SEC) confirmed the disappearance of the polysulfone peak and the appearance of a new peak in the low molecular weight region. Although only a supernatant was obtained when 10 equivalents of N-heterocyclic carbene borane were used, this confirmed the complete decomposition of the polysulfone. Even when 5 equivalents were used, partial decomposition of the polysulfone was confirmed. The SEC spectrum is shown in Figure 2. SEC measurements were performed using a size exclusion chromatography system manufactured by JASCO Corporation, with a RI-4030 differential refractive index detector, two KF-804L columns, and a KF-G4A guard column. The molecular weight profile curve was created using polystyrene. The values ​​on the horizontal axis (time) in Figure 2 are in minutes. [Industrial Applicability]

[0021] Polysulfone is expected to be used in a variety of applications. By cleaving and decomposing the sulfur-carbon bond in the presence of N-heterocyclic carbene borane, the resulting product can be not only recycled but also upcycled, making it possible to apply polysulfone to a wide range of applications.

Claims

1. A method for decomposing polysulfone by heating the polysulfone using a radical initiator, a base, and in the presence of an N-heterocyclic carbene borane in a solvent.

2. 2. The decomposition method according to claim 1, wherein the radical initiator is di-tert-butoxy peroxide.

3. 2. The method according to claim 1, wherein the base is potassium carbonate.

4. 2. The decomposition method according to claim 1, wherein the solvent is o-xylene.

5. The decomposition method according to claim 1, wherein the N-heterocyclic carbene borane is a compound represented by the following formula: 【Chemistry 1】

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